Electrode steam humidifiers have proven to be effective in adding humidity in forced-air furnace systems. The low plenum temperatures in many high efficiency furnaces, heat pumps and electric furnaces cannot provide enough heat for evaporative type humidifiers to operate properly. Despite this, prior steam humidifiers have not gained widespread acceptance, partly due to their cost and also the build up of minerals on the boiling electrodes significantly reduces their efficiency and requires frequent maintenance for conventional steam humidifiers.
Prior electronically controlled steam humidifiers have attempted to employ current detection circuitry to maintain current within a predetermined range. However, these prior humidifiers have not adequately addressed the fact that cold water is less conductive than hot water and the fact that soft water is less conductive than hard water.
Other electronically controlled steam humidifiers have been quite costly to manufacture due to the complexity and the number of costly components required. A significant cost of systems which provide flush and drain operations is associated with providing a solenoid operated drain valve in addition to the required fill valve.
Furthermore, prior art steam humidifiers have not been sufficiently reliable in handling excessive current conditions and are limited to operation only when both the humidifier senses the need for additional humidity and the furnace blower is on as dictated by the furnace circuit sensing the need for additional heat rather than in response to only the need for additional humidity without heat.
Examples of control circuits which may relate to electrode type steam humidifiers are disclosed in U.S. Pat. Nos. 3,269,364 to Higgins, 3,629,550 to Carlsson, 3,651,753 to Schmidt, 3,682,141 to Johansen, 3,761,6799 to Dall, 3,780,261 to Eaton-Williams, 3,937,920 to Gundacker et al, 3,944,785 to Eaton-Williams, 4,029,937 to Russell, 4,093,847 to Walker et al, 4,146,775 to Kirchner et al, 4,196,341 to Williams, 4,262,191 to Lepper et al, 4,347,430 to Howard-Liecester et al, 4,382,173 to Howard-Liecester, French Pat. No. 2,279,448 and German Pat. No. 2,314,474, as well as a model X-15 steam humidifier sold by Autoflo Company, a division of the assignee of the present invention, and the series of electrode humidifiers sold under the model designation Condair ES by Nortec Industries, Inc. of Ogdensburg, N.Y.